Such gripping devices, i.e. so called clamp-down grippers, are employed in container transport systems or container handling systems in mechanically controlled installations or in uncontrolled installations activated by the loading and unloading of containers. Mechanically controlled clamp-down gripping devices are known for example from EP 0 659 683A. Container operated clamp-down grippers are known from DE 297 13 510 U. The gripper devices are frequently actuated by an accumulator, for example in the swivel direction of the gripper device and the accumulator may comprise elastomer-, spiral- or compression springs.
Container transport systems, in particular bottle transport systems must satisfy high demands in regard to microbiological conditions and sanitation and must be functionally safe over an extended service life and with high work frequency rate. Because of the drawbacks of mechanical springs, the suggestion has already been made in bottle transport technology to use magnetically cooperating permanent magnets as magnetic springs, which offer benefits in regard to the microbiological conditions, sanitation and service life.
Even though permanent magnets ensure an exactly adjustable gripping force for a single gripper size of a container, they nevertheless have the drawback, the same as mechanical springs, of not generating uniform gripping forces when one and the same gripper is used for different gripper sizes of containers within a specified gripper range, based on a progressive or regressive characteristic line. It would, however, be desirable, regardless of the respective gripper size, to clamp down on each container with the same gripper force. According to experience, gripper size within the gripper range varies, for example, between diameters of approximately 24 mm to 38 mm, in particular with respect to plastic bottles such as PET bottles. Until now it has not been possible to solve the problem of altering the gripping forces for one and the same gripper device to accommodate different gripper sizes.